This invention relates to a nozzle for the refining of metals or ferroalloys by blasts of oxygen from above the melt.
The design of an oxygen blast nozzle necessitates certain computations which must take into account the following two quantities: the Mach number, and the optimum flow rate. This is regardless of whether the nozzle delivers a vertical jet for the refining operation itself; or the nozzle includes additional oblique jets for after combustion of carbon monoxide.
The Mach number is a quantity which expresses the impulse, the velocity or the intensity of the jet. The blast pipe of a nozzle usually includes a convergent portion and a divergent portion downstream of the convergent section. The Mach number is a function of the ratio of the diameters of the outlet of the divergent section and the throat of the convergent section. The optimum flow rate is a function of the inlet pressure to the blast pipe and the diameter of the throat of the convergent section.
It has been found that these two quantities depend upon the geometric configuration of the blast pipe; and do not vary independently of one another. This implies that it is not possible to effect blasting with an intense jet and reduced flow using a nozzle designed to have a large optimal flow; nor to effect blasting with a soft jet and reduced flow using a nozzle designed to have a large flow, without moving in one direction or the other away from the optimal quantities linked to the geometric configuration of the blast pipe. However, if it is attempted to exceed the limits (with respect to the flow rate and outlet speed), within the converter, just outside the mouth of the nozzle, shock waves are created. The characteristics of the jet are degraded, and nozzle wear is accelerated.
The metallurgist may wish to project onto the bath in the refining path a soft vertical jet, with a high flow rate. Such a manner of blasting is desirable in refining when a greatly oxidized slag is to be formed. It will also be appreciated that there could be a need to blast with an intense vertical jet at a reduced flow rate. This procedure would be indicated in order to reduce the total volume of oxygen supplied to the converter, so as not to oxidize the slag while at the same time ensuring a vigorous decarbonization of the metal.